Electromagnetic compatibility filter utilizing inherently formed capacitance

ABSTRACT

An electromagnetic compatibility (EMC) filter used in a hybrid technology circuit component, having current-carrying lines and a ground conductor, for protection against electromagnetic interference. The current-carrying lines and ground conductor are arranged on a ceramic plate. The current-carrying lines are covered by a dielectric, which in turn, is covered by an upper metal screen in electrical contact with the ground conductor. A lower metal screen is arranged on the ceramic plate beneath the current-carrying lines and is in electrical contact with the ground conductor.

FIELD OF THE INVENTION

The present invention relates to an electromagnetic compatibility (EMC)filter used in hybrid technology circuits. More specifically, thepresent invention relates to an EMC filter used in a hybrid componenthaving current-carrying lines and a ground conductor.

BACKGROUND OF THE INVENTION

It is generally known to protect electric or electronic devices orcircuits from line-conducted electromagnetic irradiation. For thispurpose, interference-suppression capacitors are provided, for example,which are connected via a mass frame ground connection to the circuitarrangement and via a compression spring to a metal housing. Adisadvantage of this known configuration is that, as mechanical parts,the mass springs require space. Moreover, aging of the parts can causethe spring contact to the housing to deteriorate. Also, because of thelong path between the interference-suppression capacitor and the groundconnection part, emission of interference signals can still occur.

It is further known to use an electrically conductive adhesive agentbetween the circuit arrangement and the housing to provide capacitivecoupling. German Unexamined Patent Application No. 38 37 206 describesusing an adhesive agent to couple a discrete interference-suppressioncapacitor, situated on a circuit board, to a grounded metallic housingthrough a dielectric layer, thereby creating a capacitive coupling tothe housing that is in series with the discrete capacitor on the circuitboard. Although this arrangement offers a sufficiently high-frequencycoupling of a circuit to ground, it cannot be used for hybrid circuitsand, in any case, requires an electrically conductive housing. Moreover,the additional arrangement of a chip capacitor is needed.

SUMMARY OF THE INVENTION

The present invention provides an EMC filter for use in hybridtechnology circuits, which guarantees effective protection againsthigh-frequency and low-frequency interference without requiringadditional components.

It was discovered that when current-carrying lines are surrounded by adielectric material and a metal screen which is connected to a groundconductor and is arranged on a ceramic plate, an arrangement approachingthat of a plurality of capacitors having extremely low inductance can beachieved. As a result, effective EMC protection is achievedinexpensively using standard technology.

The present invention logically combines the elements of hybridtechnology to provide EMC protection. For example, costly bushing-typecapacitors and coaxial cables can be imitated and replaced by hybridtechnology circuit arrangements in accordance with the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a first embodiment of a hybridcomponent in accordance with the present invention.

FIG. 2 is a top view of the hybrid component of FIG. 1.

FIG. 3 is a cross-sectional view of a second embodiment of a hybridcomponent in accordance with the present invention.

FIG. 4 is a cross-sectional view of a third embodiment of a hybridcomponent in accordance with the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a hybrid component comprising aceramic plate 10, and two current-carrying lines 12 situated on an uppersurface of the ceramic plate 10. The current-carrying lines 12 aresurrounded by a dielectric 14. On a bottom surface of the ceramic plate10, the hybrid component comprises a metal screen 16, which is connectedvia a plated-through hole 18 to a ground conductor 20. An additionalmetal screen 22, which covers the dielectric 14 and the ground conductor20, is arranged on the upper side of the hybrid component. The metalscreen 22 is electroconductively connected to the ground conductor 20.

The entire hybrid component is mounted on a housing part 26, which canserve at the same time as a cooling part, and if it is a metal housing,as ground.

In conjunction with the current-carrying lines 12 and the dielectric 14,the metal screen 22 forms a plurality of capacitors having extremely lowinductance and, because of the relatively thin dielectric 14, havingrelatively high capacitance. Due to the capacitive coupling of thecurrent-carrying lines 12 to the ground conductor 20, the effect ofinterference-suppression capacitors is achieved, so that high-frequencycoupling of the circuit to ground, and thus reliable interferencesuppression, is made possible.

FIG. 2 is a top view of the hybrid component whose cross-section isshown in FIG. 1. The view in FIG. 1 corresponds to the cross-sectionI--I indicated in FIG. 2. As shown in FIG. 2, discrete ceramic chipcapacitors 24 are also arranged on the hybrid component. The ceramicchip capacitors 24 offer additional capacitive coupling of thecurrent-carrying lines 12 to the ground conductor 20. This capacitivecoupling protects the circuit from low-frequency interference. As such,a combination of both types of capacitive coupling provides thecurrent-carrying lines 12 with highly effective protection against theentire spectrum of line-conducted interference.

Moreover, by having a shortest possible binding of the discrete ceramicchip capacitors 24, disturbing inductance is avoided. A completelysymmetrical coupling enables opposite-phase interferences to becompletely eliminated.

FIG. 3 is a cross-sectional depiction of a second embodiment of a hybridcomponent in accordance with the present invention. (Like parts incommon with the embodiment of FIG. 1 are shown with the same referencenumerals.) On its top surface 11, the ceramic plate 10 has a metalshield 17, on which the current-carrying lines 12 are arranged,separated from the metal shield 17 by the dielectric 14. The groundconductor 20 is electroconductively connected to the metal shield 22covering the dielectric 14. Furthermore, the ground conductor 20 alsoelectrically contacts the metal screen 17 through a cut-out 15 in thedielectric 14.

As mentioned above with respect to FIG. 1, by means of the electricallyconductive connection to the ground conductor 20 and, thus, to the metalscreen 17, and together with the current-carrying lines 12 and thedielectric 14, the metal screen 22 forms a plurality of capacitorshaving extremely low inductance and relatively high capacitance.

As explained above with respect to FIGS. 1 and 2, discrete ceramic chipcapacitors 24 (not shown in FIG. 3), which offer additional capacitivecoupling of the current-carrying lines 12 to the ground conductor 20,can also be arranged on the hybrid component of FIG. 3.

FIG. 4 is a cross-sectional view of a third embodiment of a hybridcomponent in accordance with the present invention. In this embodiment,a metal screen 19 is arranged on the bottom side 13 of the ceramic plate10. The current-carrying lines 12 and the ground conductor 20 arearranged on the top side 11 of the ceramic plate 10. Thecurrent-carrying lines 12 are capacitively coupled via discrete ceramicchip capacitors 24 to the ground conductor 20.

In the embodiment of FIG. 4, the metal screen 19, together with thecurrent-carrying lines 12 and the ceramic plate 10, constitute acapacitive coupling of the current-carrying lines 12 to the metal screen19. The ceramic chip capacitors 24 provide additional capacitivecoupling of the current-carrying lines 12 to the ground conductor 20.

Overall therefore, the above-disclosed embodiments make it possible toflexibly adapt protective arrangements to each application-specific EMCproblem. In particular, an optimal result can be achieved by variablyfitting the discrete ceramic chip capacitors 24 with components for thelow frequency range and by applying dielectric pastes having differentvalues to vary the printed capacitors for the upper frequency range.

What is claimed is:
 1. An electromagnetic compatibility filter for useon a hybrid component having current-carrying lines and a groundconductor arranged on an upper surface of a ceramic plate, the filtercomprising:a dielectric covering the current-carrying lines; a lowermetal screen in electrical contact with the ground conductor andarranged on the ceramic plate beneath the current-carrying lines; and anupper metal screen covering the dielectric and being in electricalcontact with the ground conductor, wherein the current-carrying linesare electrically insulated from the upper and lower metal screens. 2.The filter according to claim 1, wherein the lower metal screen isarranged on a bottom surface of the ceramic plate.
 3. The filteraccording to claim 2, wherein the lower metal screen is connected via aplated-through hole to the ground conductor.
 4. The filter according toclaim 1, wherein the lower metal screen is arranged on the upper surfaceof the ceramic plate and is separated from the current-carrying lines bythe dielectric.
 5. The filter according to claim 1, wherein the hybridcomponent includes at least one discrete ceramic chip capacitor havingone contact connected to the current-carrying lines and another contactconnected to the ground conductor.
 6. The filter according to claim 5,wherein the hybrid component includes at least two discrete ceramic chipcapacitors in a symmetrical arrangement.